Comprehensive Description

Description

“Marseniopsis, n. gen.

The Marseniopsides differ strikingly from the other Marseniad genera. They form a beautiful transition-link between the diclinous and the androgynous (Marsenina, Onchidiopsis) Marseniadæ, and distinctly demonstrate a unity of relationship which makes it impossible to split up the family. In their general form they agree with the Onchidiopsides; the superior part of the body is hemispherical, as if distended; the mantle margin is thick and swollen; the external mouth lies far forwards. They have, however, no right exhalent fold nor associated semi-canal, and the branchial folia rather resemble those of the Marseniæ. The mandibular plates are narrower, and, on the whole, smaller, than in other Marseniadæ. The lingual armature, on the other hand, agrees exactly with that of the androgynous forms; outside the lateral teeth there are, in addition, two hooked plates. The Marseniopsides have the sexes separate. The anatomical relations resemble most closely those of the Chelyonoti; the inferior portion of the vas deferens does not lie freely in the lower body-cavity; the penis most nearly resembles that of the Marseniæ proper. The shell is also, on the whole, like that of the typical Marseniæ.

The only representatives of the genus, as yet known, are the two new South Sea1 species about to be described.

1According to a note which I made in 1873, in the British Museum, there is a specimen there, obtained in “Sholl Bay, Strait of Magellan,” which might perhaps, belong to this genus.”